3,110 research outputs found
Non-Hermitian description of a superconducting phase qubit measurement
We present an approach based on a non-Hermitian Hamiltonian to describe the
process of measurement by tunneling of a phase qubit state. We derive simple
analytical expressions which describe the dynamics of measurement, and compare
our results with those experimentally available.Comment: 8 pages, 4 figure
Petrographic and crystallographic study of silicate minerals in lunar rocks
Optical U-stage measurements, chemical microprobe data, and X-ray procession photographs of a bytownite twin group from rock 12032,44 are compared. Sharp but weak b and no c-reflections were observed for this An89 bytownite indicating a partly disordered structure. Euler angles, used to characterize the orientation of the optical indicatrix, compare better with values for plutonic than for volcanic plagioclase. This indicates that structural and optical properties cannot be directly correlated
Decoherence of a two-state atom driven by coherent light
Recent studies of the decoherence induced by the quantum nature of the laser
field driving a two-state atom [J. Gea-Banacloche, Phys. Rev. A 65, 022308
(2002); S. J. van Enk and H. J. Kimble, Quantum Inf. and Comp. 2, 1 (2002)]
have been questioned by Itano [W. M. Itano, Phys. Rev. A 68, 046301 (2003)] and
the proposal made that all decoherence is due to spontaneous emission. We
analyze the problem within the formalism of cascaded open quantum systems. Our
conclusions agree with the Itano proposal. We show that the decoherence,
nevertheless, may be divided into two parts--that due to forwards scattering
and to scattering out of the laser mode. Previous authors attribute the former
to the quantum nature of the laser field.Comment: 6 pages, 2 figures, to appear in Phys. Rev.
Memory in the Photon Statistics of Multilevel Quantum Systems
The statistics of photons emitted by single multilevel systems is
investigated with emphasis on the nonrenewal characteristics of the
photon-arrival times. We consider the correlation between consecutive
interphoton times and present closed form expressions for the corresponding
multiple moment analysis. Based on the moments a memory measure is proposed
which provides an easy way of gaging the non-renewal statistics. Monte-Carlo
simulations demonstrate that the experimental verification of non-renewal
statistics is feasible.Comment: 5 pages, 3 figure
Asymmetric quantum dot in microcavity as a nonlinear optical element
We have investigated theoretically the interaction between individual quantum
dot with broken inversion symmetry and electromagnetic field of a single-mode
quantum microcavity. It is shown that in the strong coupling regime the system
demonstrates nonlinear optical properties and can serve as emitter of the
terahertz radiation at Rabi frequency of the system. Analytical results for
simplest physical situations are obtained and numerical quantum approach for
calculating emission spectrum is developed.Comment: Article is accepted to Phys. Rev. A (7 pages, 5 figures
Point-of-Care Manufacture: Regulatory Opportunities and Challenges for Advanced Biotherapeutics
On 29 June 2021, UCL’s Future Targeted Healthcare
Manufacturing Hub (FTHMH) held an online workshop to discuss
the concepts and rationale of a new point-of-care (POC)
manufacturing regulatory framework in development by the UK’s
Medicines and Healthcare products Regulatory Agency (MHRA).
The proposal, which seeks to address the unique challenges of
manufacturing healthcare products at, (or close to), the POC, is
anticipated for publication and public consultation in summer
2021
The Accuracy of Perturbative Master Equations
We consider open quantum systems with dynamics described by master equations
that have perturbative expansions in the system-environment interaction. We
show that, contrary to intuition, full-time solutions of order-2n accuracy
require an order-(2n+2) master equation. We give two examples of such
inaccuracies in the solutions to an order-2n master equation: order-2n
inaccuracies in the steady state of the system and order-2n positivity
violations, and we show how these arise in a specific example for which exact
solutions are available. This result has a wide-ranging impact on the validity
of coupling (or friction) sensitive results derived from second-order
convolutionless, Nakajima-Zwanzig, Redfield, and Born-Markov master equations.Comment: 6 pages, 0 figures; v2 updated references; v3 updated references,
extension to full-time and nonlocal regime
Preparation information and optimal decompositions for mixed quantum states
Consider a joint quantum state of a system and its environment. A measurement
on the environment induces a decomposition of the system state. Using
algorithmic information theory, we define the preparation information of a pure
or mixed state in a given decomposition. We then define an optimal
decomposition as a decomposition for which the average preparation information
is minimal. The average preparation information for an optimal decomposition
characterizes the system-environment correlations. We discuss properties and
applications of the concepts introduced above and give several examples.Comment: 13 pages, latex, 2 postscript figure
Non-Markovian Quantum Trajectories Versus Master Equations: Finite Temperature Heat Bath
The interrelationship between the non-Markovian stochastic Schr\"odinger
equations and the corresponding non-Markovian master equations is investigated
in the finite temperature regimes. We show that the general finite temperature
non-Markovian trajectories can be used to derive the corresponding
non-Markovian master equations. A simple, yet important solvable example is the
well-known damped harmonic oscillator model in which a harmonic oscillator is
coupled to a finite temperature reservoir in the rotating wave approximation.
The exact convolutionless master equation for the damped harmonic oscillator is
obtained by averaging the quantum trajectories relying upon no assumption of
coupling strength or time scale. The master equation derived in this way
automatically preserves the positivity, Hermiticity and unity.Comment: 19 pages, typos corrected, references adde
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